Advanced thermal barrier coating materials, generally of ceramic composition, have been developed and are being further developed for use on the combustor section hardware of high-performance gas turbine engines. To optimize the utility of such materials, accurate surface temperature measurements are required so as to better understand their responses to changes in the combustion environment; accurate temperature measurements are also necessary, moreover, to adequately evaluate engine performance, and life.
Present temperature sensors and pyrometer systems applied to combustor section hardware of turbine engines are based on the measurement of electromagnetic radiation emitted by traditional metal components (i.e., non-coherent, hot body-generated radiation) in short wavelength ranges, typically 0.4 to 1.8 xcexcm. For several reasons such systems are not well-suited for use in connection with high-performance gas turbine engines that utilize ceramic and ceramic coated materials. In particular, emittance values (which are of course necessary for making such temperature measurements) are low and variable at short wavelengths, and many of the coatings of interest are transparent to such radiation.
It is well known in the art to employ radiation pyrometers to measure the temperature of an object (e.g., rotor blades of a gas turbine engine) moving at high speed through the field of view of the pyrometer, wherein the pyrometer produces an output signal that is proportionate to the intensity of incident radiation emanating from the surface of the object. Such a pyrometer may include a detector at one end of a radiation transmission system, and an optical lens at the opposite end, as well as gating means for repetitively interrupting passage of the temperature signals. Representative systems are described, for example, in U.S. Pat. Nos. 3,855,864, 4,306,835, 4,582,426, 4,797,006, and 5,226,731.
It is also known to determine the surface temperature of an object by measuring its radiance at wavelengths at which the material exhibits strong absorption bands (resulting in the so-called xe2x80x9cChristiansen effectxe2x80x9d), thereby enabling the temperature to be determined readily and accurately (without reflection error) by correlation of the measured radiance to that of a black body at the same wavelength value. Such a technique is described in U.S. Pat. Nos. 4,985,858 and 5,239,488.
From U.S. Pat. No. 5,440,664, it is know to transmit mid-infrared radiation through a hollow waveguide. The waveguide serves for the transmission of laser radiation with low attenuation and with the preservation of good transverse spacial coherence, and is believed to be particularly adapted to transport laser radiation for biomedical/surgical applications, at a suitable power but in a non-quantitative fashion; cooling, and high-pressure features, are not believed to be required.
Accordingly, the broad objects of the present invention are to provide a radiation thermometer or pyrometer, pyrometer system, and pyrometric method adapted for accurately and rapidly measuring the temperature of hot elements, and in particular hot elements in a combustion gas environment, especially elements that are fabricated from ceramic or that carry a ceramic thermal barrier coating and that may be moving at high speed, as in a gas turbine engine.
Certain of the foregoing and related objects of the invention are attained, in accordance with the present invention, by the provision of a temperature-monitored system, and a radiation pyrometer for incorporation thereinto, wherein the system includes apparatus having structure defining a combustion chamber. The radiation pyrometer comprises, in combination:
means for collecting and transmitting electromagnetic radiation, including a hollow core waveguide having entry and exit ends, and means for directing radiation into the core of the waveguide at its entry end;
means for mounting the means for collecting and transmitting with the means for collecting disposed for receiving, and directing into the waveguide core, radiation emanating from at least one surface within the chamber;
a radiation detector that is responsive for generating electrical signals indicative of the energy of impinging radiation lying in a spectral region encompassing mid-infrared and long-infrared wavelengths, the detector being operatively connected to the exit end of the waveguide for receiving radiation transmitted through the core thereof;
radiation discriminating means for permitting substantial passage of radiation only within the designated spectral region, the discriminating means being operatively disposed for permitting substantial passage to the detector of radiation of wavelengths only within the spectral region;
data acquisition means operatively connected to receive such indicative electrical signals from the detector; and
electronic data processing means operatively connected and programmed for determining, from signals received from the data acquisition means, the temperature of the surface from which emitted radiation is collected by the collecting and transmitting means.
In preferred embodiments the designated spectral region for operation of the pyrometer will be constituted of wavelengths in the range 2 to 50, preferably 8 to 12, and most desirably 10 to 11.5 microns. In those embodiments in which the narrower ranges are employed, and the monitored surface is of a ceramic material, the data processing means will most beneficially be programmed to correlate measured spectral radiance to the radiance of a black body at wavelengths within the designated range, so as to take advantage of the Christiansen effect. Use of the narrower ranges is additionally advantageous from the standpoint of minimizing interference from water and carbon dioxide, and thus enabling accurate temperature measurements to be made in a combustion gas environment.
The means for mounting may comprise a probe body having a cavity within which at least an entry end portion of the waveguide, and the means for directing, are mounted, the probe body defining a fluid-flow space within the cavity along the means for directing and the entry end portion of the waveguide, and having means thereon for introducing a protective fluid into the fluid-flow space therewithin. The means for directing radiation will normally comprise a lens disposed adjacent the gentry end of the waveguide for focusing radiation into its core.
In especially preferred embodiments, the apparatus of the invention will comprise a gas turbine engine comprised of a housing or case defining a combustion chamber, and having at least one rotor with a multiplicity of blades thereon, driven by combustion gases. The monitored surface will comprise the surface of an internal part of the engine, most advantageously surfaces on the rotor blades, and the system will optimally be constructed to enable determinations to be made of the surface temperature of each of the blades of an engine rotor as they move through the field of view of the pyrometer probe optics.
The system may additionally include gating means operatively positioned and cyclically operational to alternatingly pass and block the transmission of a radiation beam through the waveguide core to the detector, the gating means including a black body element for blocking the radiation beam and for providing a self-calibration reference for the pyrometer. The radiation discriminating means will usually comprise a band-pass filter, and the radiation detector will typically be selected from the group consisting of MCT, InSb, and DTGS detectors, other infrared-sensitive detectors can of course be used, as well.
Additional objects of the invention are attained by the provision of a method for determining the temperature of a monitored surface in a combustion gas environment, comprising the steps:
collecting radiation, in a spectral region encompassing mid-infrared and long-infrared wavelengths, emanating from the monitored surface;
transmitting the collected radiation through the core of a hollow core waveguide to a radiation detector that is responsive for generating electrical signals indicative of the energy of impinging radiation lying in the designated spectral region; and
processing the generated signals so as to determine therefrom the temperature of the monitored surface.
Here again, the designated spectral region will usually constitute wavelengths in the range 2 to 50, preferably 8 to 12, and most desirably 10 to 11.5, microns, the narrower ranges being especially desirable when the monitored surface is comprised of a ceramic material, so as to exploit the Christiansen effect, and for making measurements in the presence of ambient combustion gases. It should be noted that the method (and apparatus) of the invention is suitable for monitoring and measuring the temperature of a surface of virtually any material, as long as the emissivity of that material is known or can be determined. The method may employ gating means, enabling self-calibration, and it may include an additional step of directly or indirectly bathing, with a protective fluid, at least the portion of the waveguide that is proximate to the monitored surface, the protective fluid serving a cooling function, a cleaning function, or both.